Streptococcus pneumoniae is a rather ubiquitous human pathogen, which can infect several organs including the lungs, the central nervous system (CNS), the middle ear, and the nasal tract. Infection results in various symptoms such as bronchitis, pneumonia, meningitis, sinus infection, and sepsis. S. pneumoniae is a major cause of bacterial meningitis in humans and is associated with significant mortality and morbidity despite antibiotic treatment (Quagliarello et al., (1992) N. Eng. J. Med. 327: 869-872).
There are two currently available pneumococcal vaccines. One is a vaccine for adults composed of 23 different capsular polysaccharides which together represent the capsular types of about 90% of strains causing pneumococcal infection. This vaccine, however, is not immunogenic in children, an age group with high susceptibility to pneumococcal infection. In adults the vaccine has been shown to be about 60% efficacious against bacteremic pneumonia, but it is less efficacious in adults at higher risk of pneumococcal infection because of age or underlying medical conditions (Fedson, and Musher. 2004. “Pneumococcal Polysaccharide Vaccine”, pp. 529-588. In Vaccines. S. A. Plotkin and W. A. Orenstein (eds.), W. B. Saunders and Co., Philadelphia, Pa.; Shapiro et al., N. Engl. J. Med. 325:1453-1460 (1991)). This vaccine has not been shown to be effective against non-bacteremic pneumococcal pneumonia, the most common form of infection.
The second available vaccine is a 7-valent conjugate vaccine that is efficacious against bacteremic pneumococcal infections in children less than 2 years of age. It has also demonstrated efficacy against pneumonia (Black et al., Arch. Pediatr 11(7):485-489 (2004)). The production of this vaccine is complicated because of the need to produce 7 different conjugates and this leads to the vaccine being expensive (about $200/child). Moreover, the vaccine does not do a good job of covering infections in the developing world where non-vaccine types of Streptococcus pneumoniae are very common (Di Fabio et al., Pediatr. Infect. Dis. J. 20:959-967 (2001); Mulholland, Trop. Med. Int. Health 10:497-500 (2005)). This vaccine does not work as well against otitis media and colonization as it does against invasive disease. It has also been shown that the use of the 7-valent conjugate vaccine has led to an increase in colonization and disease with strains of capsule types not represented by the 7 polysaccharides included in the vaccine (Bogaert et al., Lancet Infect. Dis. 4:144-154 (2004); Eskola et al., N Engl. J. Med. 344:403-409 (2001); Mbelle et al., J. Infect. Dis. 180:1171-1176 (1999)). Therefore, a need remains for effective treatments for Streptococcus pneumoniae. 